Well although 5000 is not really too high, you still need some good performance if it's going to be hot, I would narrow your decision to the only smart choices,
You asked about the EC130, Koala, and Bell 407, I would skip the 130 right away, in my experience Eurocopter can be a pain supportwise, and if you have a choice? The Koala has very good performance, speed, but it's more expensive than the 407, the latter, is proven, economical, has great performance, has great support.
Between the EC135 and the 109E there is a world in difference in performance, the Agusta being much better, I fly Power landing and taking off at altitudes between 7.5 and 8.5 K FTAMSL, it's as good as it gets.
Then I have a fried who operates the 135 at hot and high and it's marginal.